Along with development of the information society, substantial increase of the amount of information has been expected in recent years. Due to such increased information, necessity to install a lot of electronic equipment such as a server having a high information processing capacity has arisen. Generally, electronic equipment having a high information processing capacity is electronic equipment with high power consumption. In addition, because most of electric power consumed by electronic equipment becomes heat, installing electronic equipment having a high information processing capacity results in making the surrounding temperature rise due to its exhaust heat. In particular, in a data center in which a large number of electronic equipment such as servers are installed, a great deal of heat is exhausted from the electronic equipment, and the heat needs to be cooled to keep the functions of the electronic equipment. Therefore, a lot of air conditioning electric power is needed. As a consequence, a method to reduce an air conditioning load by absorbing heat of electronic equipment and transporting it to some other place is required.
As a method for absorbing heat of electronic equipment, a means for absorbing heat of electronic equipment by circulating a refrigerant using a phase change of the refrigerant without using a pump has been thought of. This method is very economical because motive power is not used for circulation of a refrigerant. In addition, when a refrigerant of an insulation property is used as an inner refrigerant, even if the inner refrigerant leaks due to damage of a certain portion, influence on electronic equipment is very small. Accordingly, the means using a phase change of a refrigerant is a very effective means for absorbing exhaust heat of electronic equipment such as servers in a data center that are not allowed to stop.
A heat absorbing means using a phase change of a refrigerant will be described simply using FIG. 1 and FIG. 2. FIG. 1 is a schematic diagram of a cooling apparatus for absorbing exhaust heat of electronic equipment 6, and FIG. 2 is a diagram of a cooling apparatus attached to a rack 5 storing the electronic equipment 6.
In the exhaust side of the rack 5 storing a lot of pieces of electronic equipment 6, a heat receiver 1 to absorb exhaust heat of the electronic equipment 6 is installed. A radiator 2 is installed above the heat receiver 1, and the heat receiver 1 and the radiator 2 are communicated with each other by two pipes of a vapor-phase pipe 3 through which a vapor-phase refrigerant passes and a liquid-phase pipe 4 through which a liquid-phase refrigerant passes. A refrigerant is sealed in the interior, and, in the heat receiver 1, external heat is received, and a liquid-phase refrigerant boils to cause a phase change to a vapor-phase refrigerant. The phase-changed vapor-phase refrigerant moves to the radiator 2 through the vapor-phase pipe 3 by the buoyancy, its heat is taken away by a cooler such as a fan and a water cooler, and it is liquefied and changes its phase to a liquid-phase refrigerant. The liquid-phase refrigerant descends by the gravity through the liquid-phase pipe 4, and flows back into the heat receiver 1.
Regarding the rack 5 into which the electronic equipment 6 such as a server is mounted, its size that is commonly used in a data center and the like is about 2 m in height. When the system shown in FIG. 2 is applied to a rack of such size, there is a problem that a refrigerant is pooled in the lower part due to the own weight of a liquid-phase refrigerant, and a refrigerant is not supplied to the heat receiver 1 in the upper side.
In order to solve this problem, there is disclosed in patent literature 1 and patent literature 2 a technology in which a heat receiver is divided into multiple pieces to make it be of multiple stages in the vertical direction, and a plurality of refrigerant distribution devices are provided in portions at which branching from each liquid-phase pipe to each of the plurality of heat receivers is made.
In this technology, a liquid-phase refrigerant flows into a refrigerant distribution device and, through a pipe provided in its lower part, the liquid-phase refrigerant is supplied to each heat receiver. When a refrigerant is supplied to each heat receiver sufficiently, overflow is caused inside the refrigerant distribution device in question, and the overflowed refrigerant passes through a pipe, which is provided in a side face of the device and which leads to a downward liquid-phase pipe, and heads for the refrigerant distribution device for supplying a refrigerant to the next heat receiver. By this structure, it becomes possible to supply a refrigerant to each heat receiver equally, and thus not to deteriorate the heat absorbing performance of the upper part of a rack.